The present invention relates to a method and device for braking rotation of an upper rotary body of a construction machine, such as crane, without swinging a lifted load, and also relates to a device for calculating the angle of inclination of the upper rotary body positioned at a given angle of rotation.
In construction machines such as crane equipped with a rotatable boom as upper rotary body, it is important to brake and stop rotation of the upper rotary body without swinging a lifted load. However, the conventional way of stopping rotation of an upper rotary body depends on manual operations by skilled operators. Accordingly, it has been earnestly demanded to reduce their work and ensure more safety.
In addition, in a crane whose rated load is variable according to the direction of rotation, there has been a need to automatically brake and stop rotation of an upper rotary body with preventing the upper rotary body from being subject to an over-load.
In view thereof, Japanese Unexamined Patent Publication No. 61-211295 discloses a device including a sensor, as observer, for measuring the swinging amount of load to thereby carry out feedback control of the speed of rotation based on measurements obtained by the sensor.
It is, however, difficult to brake and stop the rotation of an upper rotary body properly by such feedback control because the swinging amount of load with the rotation of the upper rotary body is affected by external conditions such as wind. Moreover, it is very difficult to measure the swinging amount with a high precision. Accordingly, such feedback control is considered to be impracticable.
It is desirable to brake and stop the rotation of an upper rotary body as quickly as possible. On the other hand, however, the braking of an upper rotary body at a greater deceleration causes the load and the upper rotary body itself to have greater inertia force in the direction of the rotation. Consequently, the upper rotary body is subject to a greater load in the direction of lateral bending.
Moreover, a load in the direction of lateral bending is greatly dependent on the inclination angle of the upper rotary body. Accordingly, it is very important to detect the inclination angle with a high precision when controlling the stop and rotation of an upper rotary body.
Specifically, construction machines such as cranes equipped with an upper rotary body are not always placed in a perfectly horizontal position. In the case of mobile cranes and the like, especially, the setting place is often changed, and there are many cases in which they are operated in slightly inclined positions. As operation in such inclined positions delicately gives an influence to the stability and strength of the machines, a control has been demanded which takes this influence into account.
In connection with this influence, Japanese Unexamined Patent Publication No. 59-172385 discloses a device in which the inclination angle of a crane body is detected with respect to a forward and backward direction or sideways direction of a crane, and the operation radius of the crane is changed based on the detected inclination angle.
Also, Japanese Unexamined Patent Publication No. 59-227688 discloses a device in which the inclination angle of a crane body is detected, and one of two predetermined rated loads is selected according to the detected inclination angle.
Further, Japanese Unexamined Patent Publication No. 62-13620 discloses a device including a sensor provided on an upper rotary body for detecting the inclination angle, whereby braking is applied to the upper rotary body according to the inclination angle detected by the sensor at every moment.
Such conventional technology, however, have the following problems which must be solved:
In the devices of Japanese Unexamined Patent Publication Nos. 59-172385 and 59-227688, the inclination angle of a crane body with respect to a forward and backward direction or sideways direction is detected, and the operation radius of the crane or the rated load is changed based on the detected inclination angle. However, it is not the inclination angle of the crane body which is in direct connection with the operation radius and the rated load, but it is the inclination angle of the upper rotary body, which changes with rotation. Accordingly, it could be seen to be ideal that an upper rotary body is controlled based on the inclination angle of the upper rotary body.
In the above-mentioned devices, however, an operation radius or rated load is set based on an initially detected inclination angle of the crane body. Consequently, it is difficult to carry out controls in accordance with actual rotation. Accordingly, to ensure the safety of a crane, the operation radius must be set at a greater value, or the rated load must be set at a smaller value, which results in a problem that the permissible operation range of a crane is unnecessarily limited smaller.
On the other hand, in the device of Japanese Unexamined Patent Publication No. 62-13620, the sensor for detecting the inclination angle is provided on the upper rotary body. Accordingly, the inclination angle of the upper rotary body can be directly detected at every moment. However, this device can obtain the inclination angle only at that moment of detection. Accordingly, it is difficult to carry out proper control of rotation of an upper rotary body.
For example, if the upper rotary body is inclined, the lateral bending load will act on the upper rotary body due to the inclination. Consideration of the lateral bending load involves limitation of the operational range of the upper rotary body. Accordingly, control of the upper rotary body is automatically taken so as not to go beyond the limit. In this device, in which the inclination angle of the upper rotary body is detected at every moment, the lateral bending load is calculated at every moment based on the detected inclination angle, and compared with the rated load. However, it will be seen to be too late to start the application of braking to the upper rotary body at the moment when the lateral bending load reaches the rated load. If braking is applied at that time, the upper rotary body will stop at a position beyond the position for the rated load due to the inertia force. In other words, a proper timing of braking the upper rotary body cannot be precisely found out from the direct detection of the inclination angle of the upper rotary body as stated above. Actually, it is necessary to carry out such control as starting the braking much earlier to give some leeway.
Also, the operator cannot obtain the permissible operation range of a crane beforehand. Accordingly, the operator cannot but continue his crane operation uneasily without knowing when the automatic braking will be started or how much more load can be handled in the present operation. Thus, it is very inconvenient.